Most tilt switches in use today use mercury. Mercury even in small amounts is toxic to the environment and particularly to human beings. It has been estimated that tens of millions of mercury switches are manufactured every year and thus, even though each switch contains only a small quantity of mercury, the total is significant. As a result, several states have considered banning the use of mercury switches.
In mercury tilt switches, the mercury is both the seismic mass and the electrical conductor which closes the electrical circuit. Impurities in the mercury tend to remain on the surface, thus clean liquid metal interacts with the solid metal electrical conductors to form a low-resistant conductive path from one conductor to the other.
To achieve a comparable low resistance using conventional switches, a substantial force is required between the switch contacts. This force is typically around 5 grams in order to produce contact resistances significantly below 0.1 ohms. Since tilt switches commonly operate when the tilt angle is less than 10 degrees, the mass of the seismic mass using a pivoting technology, for example, can become excessive. For example, in order to achieve a 5 gram contact force in such a system, the mass at an angle of 10 degrees would have to be approximately 30 grams. Such a switch would obviously be considerably larger than current mercury switches where the mass of the mercury is usually less than about 3 grams. Such switches, for example, could not be used interchangeably with current mercury switches. The substitution of mechanical switches in many cases would require significant design changes in devices which now use mercury tilt switches, such as emergency shutoff switches for irons, wall mounted silent switches and thermostats.
Mechanical tilt switches can also be sensitive to vibration which is less of a problem with mercury tilt switches. The presence of vibration can cause intermittent switch closures especially when the tilt switches are nearly at the marginal tilt angle.
These and other problems associated with prior art tilt switches are solved by the invention disclosed herein.